Hi,
I had a similar problem. I changed my debian 8 to devuan and received a
similar message.

When I restart the laptop I got a grub prompt and manually start devuan.

I repaired the system running grub-mkconfig -o /boot/grub/grub.cfg

Regards

On 2015-11-16 11:55, janpenguin wrote:
> Hi,
>
> I tried to install Duvuan using Devuan installer few times but all the
> attempts failed due to partitioning the hard disk, followed by GRUB
> installation at the end. So I used Debian installer (7.0 and 8.2) to
> create basic Debian system, and then upgraded to Devuan system one by
> one.
>
> The system setup was
> /dev/sda - bootable USB stick
> /dev/sdb - Hard disk
>
> [Partition disks] could not handle manual selection.
> When I chose manual, it complained "No root file system."
>
> Partition disks
> No root file system
> No root file system is defined.
> Please correct this from the partitioning menu.
>
> On 'Guided - use the largest continous free space', how dose it know the
> free space on the hard disk which is already partitioned?
>
> Guided partition kept the installationg going, but in the final stage of
> GRUB boot loader, it failed to detect the Devuan partition.
>
> Below is the error message.
>
> Install the GRUB boot loader on a hard disk
>
> Unable to install GRUB in /dev/sda
> Executing 'grub-install /dev/sda' failed.
>
> This is a fatal error.
>
> Another inconvenient issue which inherited from Debian installer is, the
> installer does not allow to change English keyboard layout from Qwerty
> to other one. In my case, I'm a full-time Colemak user. If I didn't have
> a qwerty keyboard, it would be difficult to use Devuan installer.
>
> Qwerty layout became defacto standard. But some keyboard makers offer
> Dvorak, Colemak layout for customers. This means they care about
> minorities. Debian has been ignorant or lazy about this issue.
>
> Debian supports non-Qwerty keyboard layouts though.
> # dpkg-reconfigure keyboard-configuration
> # service keyboard-setup restart
>
> Regards,
> Hughe
>
>
>
>